1. Field of the Invention
The present invention relates to an image display optical system which uses image display elements for modulating light and has an illumination optical system for illuminating the image display elements and a projection optical system for enlargedly projecting image light from the image display elements.
2. Description of the Related Art
A projection type image display apparatus has been conventionally used which uses an illumination optical system for illuminating an image display element and the image display element such as a liquid crystal display for modulating polarization of the illumination light to produce image light such that the image light from the image display element is enlargedly projected.
For example, Japanese Patent Application Laid-Open No. 10-319344 proposes an image display apparatus using a so-called reflection type image display element in which illumination light from the illumination optical system is incident on one side of the image display element and image light modulated by the image display element emits from the same side.
FIG. 21 shows the configuration of a conventional projection type image display apparatus. In FIG. 21, reference numeral 301 shows a light source, 302 a reflector, 303 a filter, 304 and 306 fly eye lenses. Reference numeral 305 shows a mirror, 307 a polarization beam splitter, 308 a color separation/combination prism, 309r, 309g, 309b image display elements, and 310 a projection lens.
An optical path IL of an illumination optical system and an optical path PL of a projection optical system are combined by the polarization beam splitter 307 to pass through the single color separation/combination prism 308.
The polarization beam splitter for combining the optical paths, however, is made from multilayer film, and if the angle of light incident on the multilayer film varies and thus deviates from a design angle (for example, 45 degrees), the efficiency is changed in separating the light into a P-polarized light component and an S-polarized light component to result in loss of light, thereby presenting a problem that the image display apparatus can only project dark images.
In addition, in the aforementioned image display apparatus, all the three image display elements 309r, 309g, and 309b are disposed in a plane including the reference axes of the illumination optical system and the projection optical system, that is, lines (axes) obtained by tracing a light ray along the center line of an illumination light flux in the illumination optical system, which presents a problem that the whole image display apparatus is likely to be increased in size in the direction of that plane.
Furthermore, when part of the illumination light is reflected on any transmission surface of a component such as the color separation/combination prism for directing the illumination light to the image display elements, the reflection may produce flare and cause a problem of the inability to obtain projected images of high quality.